Surface coverings, particularly PVC-based surface coverings, are widely used to decorate buildings or houses surfaces as they are more pleasant, more aesthetic and more comfortable than painted surfaces. However, these surface coverings, especially floor coverings, are generally produced in limited sizes that have to be joined one to the others. For this purpose, the use of a welding rod is well known. Usually, a round cross-section thermofusible welding rod is introduced in a hot-air welding device which heats the welding rod so that it penetrates into the space between two pieces of adjacent floor-covering elements and joins them together. Usually, once cooled-down, the excess of welding rod is cut off, or skived, with a “U”-shaped cutter or a similar tool (knife).
Welding rods are usually polymeric compositions having good adhesion to the covering elements to be joined, and allowing the welding rod to have flexibility at temperatures lower than the composition of the elements to be joined, while being easily cut off after welding.
For floor coverings having a multicolour decorative pattern, it has been suggested to use multicoloured welding rods. Thus, from an aesthetic point of view, the welding rod has to emulate the aspect or the pattern of the surface covering.
Generally, for PVC-based coverings, welding rods are PVC-based compositions of a single colour and are produced by extrusion. However, extruded coloured welding rods appear as a seam of a contrasting colour creating a discontinuity in the decorative pattern, as they are unable to properly reproduce a complex multicoloured pattern.
To address this issue and to maintain the continuity of decorative pattern, welding rods can comprise the coloured particles or granules of the surface covering the rods have to join. However, a welding rod composition comprising such particles, generally hard particles, can not be extruded without damaging the extrusion device, making thus such welding rods hard to obtained by extrusion. Therefore, for floor coverings, U.S. Pat. No. 5,635,266 has proposed a PVC-based and patterned welding rod obtained by preparing a sheet of coloured vinyl granules, colour-matched to the flooring that is to be seamed and with pigmented granules, by cutting strips of this sheet and by placing them in a mold and compressing them to form half-round rods.